Roll Observatory packages and add a roll script

packages/source_span/test/utils_test.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:source_span/src/utils.dart';
+
+main() {
+  group('find line start', () {
+    test('skip entries in wrong column', () {
+      var context = '0_bb\n1_bbb\n2b____\n3bbb\n';
+      var index = findLineStart(context, 'b', 1);
+      expect(index, 11);
+      expect(context.substring(index - 1, index + 3), '\n2b_');
+    });
+
+    test('end of line column for empty text', () {
+      var context = '0123\n56789\nabcdefgh\n';
+      var index = findLineStart(context, '', 5);
+      expect(index, 5);
+      expect(context[index], '5');
+    });
+
+    test('column at the end of the file for empty text', () {
+      var context = '0\n2\n45\n';
+      var index = findLineStart(context, '', 2);
+      expect(index, 4);
+      expect(context[index], '4');
+
+      context = '0\n2\n45';
+      index = findLineStart(context, '', 2);
+      expect(index, 4);
+    });
+
+    test('found on the first line', () {
+      var context = '0\n2\n45\n';
+      var index = findLineStart(context, '0', 0);
+      expect(index, 0);
+    });
+
+    test('not found', () {
+      var context = '0\n2\n45\n';
+      var index = findLineStart(context, '0', 1);
+      expect(index, isNull);
+    });
+  });
+}
+
+_linearSearch(list, predicate) {
+  if (list.length == 0) return -1;
+  for (int i = 0; i < list.length; i++) {
+    if (predicate(list[i])) return i;
+  }
+  return list.length;
+}